Had my coronet in the trans shop to replace a leaky front seal on a trans they rebuilt 2 years ago. Street/ strip coronet, ~550 flywheel hp. Drvoe the car for 3 seasons per year, 3 trips to the strip. He said the rear clutchpack was fried, but the other were ok. Had "blue" clutches in it, he's replacing them with reds. $470.- Any ideas what could have happened?

Check your wording.
In a torqueflite transmission, the front clutch engages with 3rd gear. This is sometimes referred to as the direct clutch because 3rd gear is direct drive, ie 1 to 1 ratio.

The rear clutch is engaged in all forward gears (1,2,3) and stays applied during shifts. It is sometimes referred to the forward clutch (not to be confused with front). If this clutch pack is burned up, it usually is due to a failure in the transmission (seal, rings, etc). In a properly working transmission, these should look like new year after year, after year...

HOW did the car react when you put it in reverse ? ...

Could be the rear drum piston seal. It won't hold the clutch pack if it goes, they'll slip and overheat but I'm no expert

The caveat is "I'm no expert" Seriously though, thanks, I've learnt something

What is fried? Blue clutches always get dark. What do the steels look like? As mentioned the clutch piston seals, rolled or torn,reaction shaft support rings worn,(also check where they ride on the drum),incorrect clutch plate clearance,valve body problem would be the most common failures. This is assuming that we are talking about the direct clutch which is only applied in high and reverse.
Doug

A strong Reverse isn't always a good indicator of front clutch sealing, the line pressure triples in Reverse so a weak clutch will often perform well at the higher pressure.

I just had the same problem on my truck, the piston retainer was cracked in four places. Letting presure escape and not apply enough to the piston to keep the clutches from spinning. Smoked the clutches and steels..It wasnt hard to see the cracks once the piston was removed. I thank god I found it now then later on the road...Phill

Sorry, guys,

The 3rd gear clutch pack was glazed over, not completely fried. The trans guy did not like the look of it, so he went from blue clutches to reds. He also said there was a "wave" rings in there and he replaced it with a snap ring, supposedly stronger.

You can tell I don't know S**T about tflites.

now they are saying the leak I went in for originally may be due to a cracked converter???